Unless I totally misread/remember incorrectly, it was the scadrians who were the first ones to give the cinder king the cinder hearts. With it being further into the space age so that the scadrians are able to travel there by ship, I wonder if in that time Harmony has slipped in Discord. The cinder hearts are a result/by product of that change. I think we all look at the different shards as good and bad, but I think it has more to do with power. The charred are seen as "bad" and Discord is typically mentioned as good mainly from the phrase "His name shall be Discord, yet they shall love him for it." But I think it has less to do with good and bad investiture and who is wielding power that makes it for good or evil.
Another theory that the scadrians are aware of Discord and know the cinder hearts come from him, so they gave them out further sow discord. (Although this conflicts with their supposed stated reason for being there and just observing)